Definitions for Water Treatment
- activated sludge process
- degradation of waste in water by microorganisms in a well aerated tank, the end products
being solid microbial biomass, and CO2
- anaerobic digestion
- bacterial digestion in absence of oxygen. Carbon content of the waste is converted to
methane rather than carbon dioxide. The methane is often used to power the treatment
plant.
- available chlorine, free and combined
- HOCl and OCl- are classed as 'free chlorine', and are powerful disinfectants.
These react with ammonia to form chloramines, 'combined chlorine', which is also
disinfectant, but weaker. The typical 'chlorine' odor and taste of water is due more to
chloramines than chlorine.
- biological reactor
- support system with a coating of biomass to developed on the surface. The
surface is in contact with both the water being treated and with air. These are classed as
fixed film biological treatment systems. Trickling filters and rotating reactors are
examples.
- cementation
- the spontaneous process of deposition of a metal on the surface of a more electroactive
metal. (e.g. Ag+ + Cu(s) --> Ag(s) + Cu+)
- chemically stabilized water
- water with pH, [Ca2+], and alkalinity adjusted to a point close to saturation
with CaCO3, which will neither precipitate solid scale in pipes nor remove the
coating of CaCO3 which protects pipe surfaces. Note that these factors are
interrelated and all will change if one changes.
- coagulation
- removal of colloidal particles by sorbing these particles in a gelatinous precipitate,
usually aluminum hydroxide, iron hydroxide or sodium silicate.
- disinfection by-products
- especially important in this category are the chlorinated organics fromed when organic
compound are not entirely oxidized by chlorine. Trichloromethane, chlorinated aldehydes,
carboxylic acids and other chlorinated compounds may be more dangerous than the original
organics.
- electrodeposition
- reduction of metal at a cathode will result in deposition of solid metal, removing it
from solution.
- electrodialysis
- water containing salt is placed between semipermeable membranes and a curent is applied.
Cations and ions migrate in opposite directions and pass through the membranes, leaving
purer water between the membrane filters.
- microstraining
- filtration through very fine steel mesh, which can remove particles down to 5-15
micrometers in diameter
- denitrification
- nitrogen as ammonia or organic nitrogen is removed from sewage because it is an algal
nutrient. Ammonium ion can be removed by raising pH above 11.5 and air stripping the
ammonia formed. Under aerobic conditions, bacteria will convert ammonia to nitrate, which
can be further reduced to nitrogen by a bacterially catalyzed reduction with an organic
source of carbon such as methanol
- reverse osmosis
- under pressure water can be forced through a semipermeable membrane, removing salts
which cannot pass the membrane
- secondary waste treatment
- removal of organic matter which contributes to BOD from sewage
- sedimentation
- removal of solids from water by allowing them to settle under gravity
- tertiary waste treatment
- a final step in treatment which targets further removal of fine particles, dissolved
organics and and dissolved inorganic materials especially algal nutrients
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